Effects of Zeranol upon luteal maintenance and fetal development in peripubertal gilts

Eighty gilts were utilized to determine whether zeranol implants could maintain hCG-induced corpora lutea (CL) in peripubertal gilts and to examine the effects of a Zeranol implant on fetal development. Crossbred gilts (171+/-0.3 days of age, 109.1+1.4 kg) were blocked by weight and ancestry to control (n=40) or treatment (n=40) groups. To induce ovulation and CL maintenance, treated gilts received 500 IU of hCG i.m. and a Zeranol ear implant (Ralgro, 36 mg; day 0). All gilts were checked once daily for estrus with a mature boar from days 3-58 of the experiment. On day 42, treated gilts received two 10 mg injections of Lutalyse (PGF(2)alpha) spaced 6 h apart. Treated gilts not displaying estrus within 7 days of PGF(2)alpha received two additional 10 mg of PGF(2)alpha spaced 6 h apart on day 49. On days 44-58, gilts detected in estrus were inseminated twice, 24 h apart with pooled semen via AI. Blood samples were obtained on days 0, 7, 18 and 42 and analyzed for serum progesterone (P(4)). Bred gilts were slaughtered on days 58-62 of gestation. Ovulation, as determined by serum concentrations of P(4) on day 7 of the experiment, was induced by hCG in 79.5% of treated gilts. Zeranol implants, however, failed to increase (P>0.05) the proportion of gilts available for breeding (treated, 21/39; control, 18/40). Of gilts inseminated on days 44-58, 16/21 treated gilts and 16/18 control gilts were pregnant at slaughter on days 58-62 of gestation. Number of fetuses (7.5 versus 12), fetal weight (83 versus 121 g), fetal length (117 versus 132 mm) and fetal survival (45% versus 78%) were reduced (P<0.001) by Zeranol implants. These data indicate that treatment of peripubertal gilts with a 36 mg Zeranol implant did not increase the proportion of gilts available for breeding while causing deleterious effects upon the fetuses.     

Effect of prior FSH treatment on the estrus and ovulation responses to eCG in prepubertal gilts

The objective of this study was to determine the effect of pre-treatment of prepubertal gilts with FSH on the estrus and ovulatory responses to eCG injection at two ages. A total of 149 prepubertal Hypor gilts were selected at 150 days (n=76) or 180 days (n=73) of age and assigned to injection of 400 IU eCG plus 200 IU hCG (PG600), 600IU eCG alone (Folligon), pre-treatment with 72 mg FSH (Folltropin) administered as 6 x 12 mg injections at 12 h intervals with 600 IU Folligon 12h after last FSH injection, or non-injected controls. To facilitate detection of estrus, gilts were exposed to a mature boar for 15 min daily for 7 days. To determine ovulatory responses, blood samples were obtained on the day of injection and 10 days later and assayed for progesterone content. Following treatment at 150 days, one control gilt (5.3%) was deemed estrus but ovulation did not occur. Compared to treatment with Folligon alone, PG600 injection tended (P=0.1) to increase the estrus response (52.6% compared with. 26.3%) and increased (P<0.01) the ovulatory response (89.5% compared with. 47.4%). The estrous response in gilts pretreated with Folltropin was intermediate (42.1%) but the ovulatory response (47.4%) was the same as for Folligon alone. Following treatment at 180 days, two control gilts (10.5%) were deemed estrus and ovulation did occur in these gilts. There was no difference between hormone-treated groups for estrus or ovulatory responses, although the ovulatory response of PG600-treated gilts tended (P=0.1) to be greater than for the Folligon-treated group (89.5% compared with 66.7%), with Folltropin-pretreated gilts being intermediate (76.5%). These data demonstrate that the estrus and ovulatory responses of gilts were greater for PG600 than for Folligon and that while responses to PG600 were not affected by gilt age, for the combined Folligon groups, estrous response (P<0.02) and ovulatory response (P<0.05) improved with increased gilt age.     

The effect of luteinizing hormone, human chorionic gonadotropin and adrenocorticotropic hormone on puberty in gilts reared in confinement

Three trials were conducted to determine the effect of human chorionic gonadotropin (HCG), luteinizing hormone (LH) and adrenocorticotrophic hormone (ACTH) on the incidence of estrus in gilts which were reared in confinement, relocated and exposed to a boar. In trial 1, 33 gilts were given saline or 250 IU HCG at an average age of 191 days and then relocated and observed for estrus twice daily for 10 days. Treatment with HCG did not increase the proportion of gilts that exhibited estrus. In trial 2, 42 gilts were relocated at an average age of 200 days. The gilts were assigned to three treatment groups and injected with saline, 68 mug LH or 1 mg LH. After 10 days of estrous detection, a laparoscopic examination of the ovaries was conducted on all gilts failing to exhibit estrus. In groups 1 to 3, the proportions of gilts exhibiting estrus or ovulating during the 10 days after treatment were 13 of 21, 6 of 10, and 5 of 11, respectively. In trial 3, 12 gilts were relocated to pasture lots, given saline or 80 IU ACTH twice daily for 2 days and checked for estrus for 14 days. The proportions of gilts that exhibited estrus after the administration of saline or ACTH were 4 of 6 and 6 of 6, respectively. The results indicate that the incidence of estrus in gilts reared in confinement, relocated and exposed to a boar was not affected by pre-treatment with exogenous HCG, LH or ACTH.     

Efficacy of exogenous gonadotrophic hormones to induce estrus in anestrous gilts

The objective of this study was to examine the response of anestrous gilts to injections of pregnant mare's serum gonadotrophin (PMSG) alone or in combination with human chorionic gonadotrophin (hCG). One hundred and eighty gilts which had failed to exhibit estrus by about 33 wk of age were given one of the following treatments: no injection, 500 IU PMSG, 1000 IU PMSG or 400 IU PMSG + 200 IU hCG. A greater number of gilts injected with 1000 IU PMSG exhibited estrus within nine days of treatment than control gilts (21/37 vs 13/41, X(2) = 5.0, P<0.05). In addition, gilts injected with 1000 IU PMSG exhibited oestrus significantly earlier than gilts receiving the other treatments. In comparisons of the proportion of gilts ovulating within 9 d of treatment and the treatment-to-ovulation interval, there were no significant differences between the three exogenous hormone treatments. There was also no significant effect of treatment on farrowing rate or subsequent litter size. The results of our study indicate that treatment of anestrous gilts with 1000 IU PMSG effectively induces ovulation and fertile estrus. Inadequate expression of estrus often accompanied the ovulation induced by the lower dosages of PMSG used with and without hCG in this experiment.     

Pituitary and ovarian hormone secretion and ovulation in gilts injected with gonadotropins during and after oral administration of progesterone agonist (Altrenogest)

We determined changes in plasma hormone concentrations in gilts after treatment with a progesterone agonist, Altrenogest (AT), and determined the effect of exogenous gonadotropins on ovulation and plasma hormone concentrations during AT treatment. Twenty-nine cyclic gilts were fed 20 mg of AT/(day X gilt) once daily for 15 days starting on Days 10 to 14 of their estrous cycle. The 16th day after starting AT was designated Day 1. In Experiment 1, the preovulatory luteinizing hormone (LH) surge occurred 5.6 days after cessation of AT feeding. Plasma follicle-stimulating hormone (FSH) increased simultaneously with the LH surge and then increased further to a maximum 2 to 3 days later. In Experiment 2, each of 23 gilts was assigned to one of the following treatment groups: 1) no additional AT or injections, n = 4; 2) no additional AT, 1200 IU of pregnant mare's serum gonadotropin (PMSG) on Day 1, n = 4); 3) AT continued through Day 10 and PMSG on Day 1, n = 5, 4) AT continued through Day 10, PMSG on Day 1, and 500 IU of human chorionic gonadotropin (hCG) on Day 5, n = 5; or 5) AT continued through Day 10 and no injections, n = 5. Gilts were bled once daily on Days 1-3 and 9-11, bled twice daily on Days 4-8, and killed on Day 11 to recover ovaries. Termination of AT feeding or injection of PMSG increased plasma estrogen and decreased plasma FSH between Day 1 and Day 4; plasma estrogen profiles did not differ significantly among groups after injection of PMSG (Groups 2-4). Feeding AT blocked estrus, the LH surge, and ovulation after injection of PMSG (Group 3); hCG on Day 5 following PMSG on Day 1 caused ovulation (Group 4). Although AT did not block the action of PMSG and hCG at the ovary, AT did block the mechanisms by which estrogen triggers the preovulatory LH surge and estrus.     

Influence of time of insemination relative to ovulation and frequency of insemination on gilt fertility

The objectives of this study were to determine the optimal time of insemination in the pre-ovulatory period (from 32 to 0 h before ovulation) and to evaluate once-daily versus twice-daily inseminations in gilts. In Experiment 1, pre-puberal gilts (n=102) were observed for estrus every 8h and ultrasonography was performed every 8h from the onset of estrus to confirmation of ovulation. The gilts were inseminated once with 4 x 10(9) spermatozoa at various intervals prior to ovulation. Pregnancy detection was conducted 24 days after AI and gilts were slaughtered 4-6 days later. Corpora lutea and the number of viable embryos were counted and the embryo recovery rate was calculated (based on the percentage of corpora lutea). Inseminations performed <24h before ovulation resulted in a higher embryo recovery rate (P=0.02) and produced 2.1 more embryos (P=0.01) than inseminations >or=24h before ovulation. However, the pregnancy rate was reduced when inseminations were performed >16 h before ovulation (P=0.08). In Experiment 2, pre-puberal gilts (n=105) were observed for estrus every 12h and ultrasonography was performed every 12h from the onset of estrus to confirmation of ovulation. Gilts were inseminated (with 4 x 10(9) spermatozoa) 12h after the onset of estrus, with inseminations repeated either every 12h (twice-daily) or 24h (once-daily) during estrus. The gilts were allowed to farrow. There were no differences (between gilts bred twice-daily versus once-daily) for return to estrus rate (P=0.36) and adjusted farrowing rate (P=0.19). However, gilts inseminated once-daily had 1.2 piglets less than those inseminated twice-daily (P=0.09). In conclusion, gilts should be inseminated up to 16 h before ovulation, as intervals >16 h reduced pregnancy rate and litter size.     

Influence of the presence of a mature female on puberty attainment in gilts

At 90 days of age, 40 Large White gilts were assigned to one of two treatments. At 155 days, a mature female which was left intact (Treatment I) or ovariectomized (Treatment O) was placed in each pen of five experimental gilts. From 180 days, estrus was checked daily with the back pressure test, and the occurrence of ovulation was detected by measuring the concentration of plasma progesterone at weekly intervals. From 240 days, a mature boar was introduced, for 5 minutes daily, into each pen during estrus detection. Gilts were slaughtered within 12 days after ovulation or at 270 days of age if they were not cyclic earlier. The percentage of gilts reaching puberty before 225 days of age was significantly higher in Treatment I (7 19 ) than in Treatment O (0 19 ) even though the average age at puberty was similar (I, 231 +/- 24 days; O, 243 +/- 12 days; mean +/- SD). Age at puberty and the number of days between mature female introduction and puberty differred significantly between the pens of gilts in Treatment O but not in Treatment I. Ovarian weights, ovulation rate and percentage of gilts with silent estrus were similar in the two treatments. Thus, the occurrence of pubertal estrus may be influenced by contact with an older, cyclic female or with other contemporary females raised in the same pen.     

Increased ovulation rate in gilts after oral administration of epostane

In Phase I of this study to enhance ovulation rate and hence litter size, gilts received 0 (sham control), 0.625, 1.25, 2.5 or 5.0 mg epostane/kg body weight on Days 10, 11 and 12 of the oestrous cycle (5 gilts/group). After epostane treatment, plasma progesterone concentrations were reduced (P less than 0.01) in a dose-related manner, % progesterone decline = 21.30 x square root of (dose) + 10.45, R2 = 0.70, but recovered to pretreatment levels by 24 h. In Phase II the effects of epostane on ovulation rate and litter size were tested at two study centres. At each centre 108 gilts were treated with the same doses of epostane as used in Phase I and the doses were given for 7 days (Days 15-21) or 12 days (Days 10-21) during the first oestrous cycle. Gilts were inseminated twice during the oestrus after treatment and were slaughtered 30 days later. Mean (+/- s.d.) ovulation rate was 16 +/- 2.7 (N = 8) and 21 +/- 4.0 (N = 61) for control and epostane-treated gilts in Centre A and 12 +/- 2.4 (N = 5) and 17 +/- 3.8 (N = 55) respectively in Centre B (P less than 0.01 for both) and was dose related (ovulation rate = 3.38 x square root of (dose) + 16.17, R2 = 0.31). The effects of 7- or 12-day epostane treatment on ovulation rate were not different (P greater than 0.05), indicating that effects of treatment after Day 14 of the oestrous cycle are most important to subsequent ovulation frequency.(ABSTRACT TRUNCATED AT 250 WORDS)     

A study of prostaglandin F2α as the luteolysin in swine: I. Effect of prostaglandin F2α in hysterectomized gilts

Experiments were conducted to determine if prostaglandin F_2α (PGF_2α) is luteolytic in swine. In Experiment 1, four bilaterally hysterectomized gilts were injected with PGF_2α at 0800 (10mg) and 2000 hours (10mg) and four gilts received .9% saline at the same times on day 17 after onset of estrus. Treatments were reversed in the two groups of gilts 21 days later. All eight PGF_2α treated gilts exhibited estrus an average of 88.0 ± 13.5 hours after treatment and average duration of estrus was 66.0 ± 16.4 hours. Saline treated controls did not exhibit estrus. Two additional gilts were hysterectomized bilaterally and the saphenous artery catheterized on day 7 after onset of estrus. PGF_2α injected on day 17 resulted in a precipitous decline in plasma progestin concentration and onset of estrus by 110 and 90 hours in gilts 1 and 2, respectively. Another bilaterally hysterectomized gilt, with CL marked with India ink, received PGF_2α on day 17. Estrus occurred 92 hours later and, on day 4, regression of marked CL to corpora albicantia and presence of newly formed CL was confirmed at laparotomy.In Experiment 2, 12 bilaterally hysterectomized gilts were treated with PGF_2α at 0800 (10mg) and 2000 hours (10mg) on either day 8, 11, 14 or 17 after onset of estrus. None of the gilts treated on days 8 and 11 exhibited estrus. Two of three gilts treated on day 14 and all three gilts treated on day 17 exhibited estrus at an average of 116.0 ± 9.8 hours post-treatment. Average duration of estrus was 49.6 ± 8.8 hours.     

A comparison of 1- and 2-cell ova production by F2 50% Meishan versus F1 White line gilts

The objective of this study was to compare recovery of pronuclear and 2-cell ova from F2 50% Meishan (MX) gilts versus F1 White line (L42) gilts. Sexually mature MX and L42 gilts were allocated across 2 treatments: Super (MX:n=9; L42:n=10) and Control (MX:n=6; L42:n=5) in a 2 x 2 factorial experiment. Allyl trenbolone (AT) was used to synchronize estrus in all gilts. Super gilts were given pregnant mare serum gonadotropin (PMSG: 1250 IU) at 24 h after AT withdrawal. Eighty-five hours after PMSG administration, all Super gilts received 750 IU of human chorionic gonadotropin (hCG). Super gilts which exhibited estrus within 24 h of hCG administration (MX-Super: n=6; L42-Super: n=5) and all Control gilts were bred naturally to Line 3 boars at 12 and 24 hours after the onset of estrus. Ova were recovered from Super gilts between 60 and 64 h after hCG and Control gilts at 48 h after the onset of estrus. All 1- and 2-cell ova were centrifuged at 15000 x g and observed using differential interference contrast microscopy. The mean ovulation rate was greater (P<0.05) for both MX-Super and L42-Super gilts in comparison to their respective Control groups. No differences were detected in the mean ovulation rate (P>0.38) or the mean number of 1- and 2-cell ova recovered (P>0.50) between MX-Super and L42-Super gilts. The proportion of 1- and 2-cell ova which exhibited visible pronuclei or nuclei was also similar among MX-SUPER and L42-SUPER gilts. This study demonstrates that MX gilts respond/perform comparably to L42 gilts with respect to estrus synchronization, superovulation, ova yield, and the ease of visibility of pronuclei or nuclei in the ova.     

Effects of parity and synchronization of donors by an oral progestogen on embryo transfer in swine

The aim of this study was to establish whether the quantity or quality of embryos collected is affected by 1) the reproductive status of donors (nulliparous gilts vs parous sows); 2) pretreatment of donors with Oxolven. Embryos were collected from gilts (n=38) and from weaned sows (n=35). Approximately half of each group (gilts and sows) had been subjected to oral treatment with the progestogenic 19-nortestosterone derivative Oxolven for 14 to 21 days. After induction of estrus with pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG) and following artificial insemination, the embryos were recovered surgically. The ovulation rate of donors averaged 21.6, with no significant difference among groups. Most of the ova and embryos collected were at the 4-cell stage (53%). There was a high incidence of uncleaved ova (28%) in both groups of animals. This was particularly so in gilts, both the Oxolven-treated and controls (35 and 32%). The incidence of uncleaved ova was lower, however, in Oxolven-treated (29%) and control sows (14%). Embryos at the 4- to 8-cell stage were transferred to synchronous recipient gilts. Transfer results, expressed by the survival of transferred embryos, were not significantly affected by the progestogen treatment (30% for Oxolven treatment vs 34% for the controls) or by the reproductive status of the donors (33% for gilts vs 28% for sows).     

Failure of the orally active progestin, Regu-mate, to overcome confinement-induced delayed puberty in gilts

Thirty-three crossbred gilts that were raised in total confinement were randomly allotted to two adjacent pens in a finishing unit at 144.7 +/- .5 days of age and 58.0 +/- 1.7 kg body weight. At approximately 253 days of age, 16 gilts were group fed a daily dose of 20 mg of Regu-mate per gilt for 18 days and 17 control gilts were group fed the same diet without Regu-mate for 18 days. Ovarian morphology was examined on 11 or 12 days after the last feeding of Regu-mate. Based on estrous behavior and ovarian morphology only one Regu-mate gilt displayed an estrus but did not ovulate and only three of the control gilts displayed estrus and ovulated at least once before the start of treatment. Three of the 16 Regu-mate gilts displayed estrus and ovulated 7.3 +/- .3 days after the last feeding and within the same time period the 3 control gilts, which previously displayed estrus, continued to have estrous cycles. One additional control gilt displayed estrus and ovulated 5 days after the last feeding of the control diet. Therefore, the proportion of gilts that displayed estrus and ovulated by the end of the experimental period were similar for the treated (25.0%) and control (23.5%) groups. Based on these results we conclude that treatment of gilts in a state of confinement-induced delayed puberty with 20 mg Regu-mate daily for 18 days failed to result in a synchronized onset of puberty in a significant proportion of gilts.     

Influence of stage of the estrous cycle on endogenous opioid modulation of luteinizing hormone, prolactin, and cortisol secretion in the gilt

Fourteen gilts that had displayed one or more estrous cycles of 18-22 days (onset of estrus = Day 0) and four ovariectomized (OVX) gilts were treated with naloxone (NAL), an opiate antagonist, at 1 mg/kg body weight in saline i.v. Intact gilts were treated during either the luteal phase (L, Day 10-11; n = 7), early follicular phase (EF, Day 15-17; n = 3), or late follicular phase (LF, Day 18-19; n = 4) of the estrous cycle. Blood was collected at 15-min intervals for 2 h before and 4 h after NAL treatment. Serum luteinizing hormone (LH) concentrations for L gilts averaged 0.65 +/- 0.04 ng/ml during the pretreatment period and increased to an average of 1.3 +/- 0.1 ng/ml (p less than 0.05) during the first 60 min after NAL treatment. Serum prolactin (PRL) concentrations for L gilts averaged 4.8 +/- 0.2 ng/ml during the pretreatment period and increased to an average of 6.3 +/- 0.3 ng/ml (p less than 0.05) during the first 60 min after NAL treatment. Serum PRL concentrations averaged 8.6 +/- 0.7 ng/ml and 7.6 +/- 0.6 ng/ml in EF and LF gilts, respectively, prior to NAL treatment, and decreased (p less than 0.05) to an average of 4.1 +/- 0.2 ng/ml and 5.6 +/- 0.4 ng/ml in EF and LF gilts, respectively, during the fourth h after NAL. Naloxone treatment failed to alter serum LH concentrations in EF, LF, or OVX gilts and PRL concentrations in OVX gilts.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of time of ovulation and sperm concentration on fertilization rate in gilts

In normal production practices, sows and gilts are inseminated at least twice during estrus because the timing of ovulation is variable relative to the onset of estrus. The objective of this study was to determine if a normal fertilization rate could be achieved with a single insemination of low sperm number given at a precise interval relative to ovulation. Gilts (n=59) were randomly assigned to one of three treatment groups: low dose (LD; one insemination, 0.5 x 10(9) spermatozoa), high dose (HD; one insemination, 3 x 10(9) spermatozoa) or multiple dose (MD; two inseminations, 3 x 10(9) spermatozoa per insemination). Twice daily estrus detection (06:00 and 18:00 h) was performed using fenceline boar contact and backpressure testing. Transrectal ultrasonography was performed every 6 h beginning at the detection of the onset of standing estrus and continuing until ovulation. Gilts in the LD and HD groups were inseminated 22 h after detection of estrus; MD gilts received inseminations at 10 and 22 h after detection of estrus. Inseminations were administered by using an insemination catheter and semen was deposited into the cervix. The uterus was flushed on Day 5 after the onset of estrus and the number of corpora lutea, oocytes, and embryos were counted. Time of insemination relative to ovulation was designated as 40 to >24 h, 24 to >12 h, and 12 to 0 h before ovulation and >0 h after ovulation. The LD gilts had fewer embryos (P<0.04), more unfertilized oocytes (P<0.05) and a lower fertilization rate (P<0.07) compared to MD gilts. The effects of time of insemination relative to ovulation and the treatment by time interaction were not significant. We conclude that a cervical insemination with low spermatozoa concentration may not result in acceptable fertility even when precisely timed relative to ovulation.     

Effects of progesterone pretreatment on fertility of gilts mated at an induced pubertal estrus

The effects of progesterone (100 mg/d, im) on pubertal fertility were examined in 247 gilts over 3 experiments. In the first experiment, 128 gilts were exposed to progesterone for 0, 2, 4 or 8 d before receiving PMSG (750 IU) 1 d later. The number of large (>4mm) follicles or corpora lutea (CL) were determined on the day of PMSG injection, Day 0 (onset of estrus), Day 1 or Day 10 (n=8). In the second experiment, embryonic survival was observed in 68 gilts after induction of estrus with PG600 (400 IU PMSG, 200 IU hCG). Vehicle or progesterone was previously administered for 2 d to these gilts, and they were allowed 1, 2, or 3 d between the last progesterone injection and PG600. In Experiment 3, a field trial was conducted in which 51 gilts received vehicle or progesterone for 2 d, followed by a 3-d interval before injection of PG600 to induce estrus. The gilts were allowed to farrow. Treatment with progesterone 1 d before PMSG increased (P<0.05) the number and size of preovulatory follicles and increased (P<0.05) the number of corpora lutea. However, the percentage of gilts pregnant by Day 10, the number of embryos recovered per gilt and embryonic survival were reduced (P<0.05) with progesterone pretreatment. Utilizing a smaller dose of PMSG (750 vs 400 IU) with PG600 negated the effects of progesterone pretreatment on ovulation rate. When the interval between progesterone treatment and PG600 was lengthened to 3 d embryonic survival to Day 30 improved but was similar to that of the vehicle/PG600 treated gilts. Fertility, as defined as conception rate and litter size, was similar between gilts exposed to vehicle or progesterone. These results indicate that pretreatment with progesterone up to the day before PMSG might improve follicular development and ovulation rate at the pubertal estrus with a dose of 750 IU of PMSG but not with the 400 IU (PG600). Reducing the dose of PMSG to 400 IU and allowing for 3 d between progesterone and gonadotropin treatment reduced the incidence of uterine infections but resulted in a fertility rate similar to that of gilts receiving PG600 alone.     

Synchronization of ovulation in cyclic gilts with porcine luteinizing hormone (pLH) and its effects on reproductive function

The overall objective was to evaluate the use of porcine luteinizing hormone (pLH) for synchronization of ovulation in cyclic gilts and its effect on reproductive function. In an initial study, four littermate pairs of cyclic gilts were given altrenogest (15 mg/d for 14 d). Gilts received 500 microg cloprostenol (Day 15), 600 IU equine chorionic gonadotropin (eCG) (Day 16) and either 5mg pLH or saline (Control) 80 h after eCG. Blood samples were collected every 4h, from 8h before pLH/saline treatment to the end of estrus. Following estrus detection, transcutaneous real-time ultrasonography and AI, all gilts were slaughtered 6d after the estimated time of ovulation. Peak plasma pLH concentrations (during the LH surge), as well as the amplitude of the LH surge, were greater in pLH-treated gilts than in the control (P=0.01). However, there were no significant differences between treatments in the timing and duration of estrus, or the timing of ovulation within the estrous period. In a second study, 45 cyclic gilts received altrenogest for 14-18d, 600 IU eCG (24h after last altrenogest), and 5mg pLH, 750 IU human chorionic gonadotropin (hCG), or saline, 80 h after eCG. For gilts given pLH or hCG, the diameter of the largest follicle before the onset of ovulation (mean+/-S.E.M.; 8.1+/-0.2 and 8.1+/-0.2mm, respectively) was smaller than in control gilts (8.6+/-0.2mm, P=0.05). The pLH and hCG groups ovulated sooner after treatment compared to the saline-treated group (43.2+/-2.5, 47.6+/-2.5 and 59.5+/-2.5h, respectively; P<0.01), with the most synchronous ovulation (P<0.01) in pLH-treated gilts. Embryo quality (total cell counts and embryo diameter) was not significantly different among groups. In conclusion, pLH reliably synchronized ovulation in cyclic gilts without significantly affecting embryo quality.     

The effects of administration of gonadotrophins and estrogens on prenatal survival in gilts

In gilts ovulation occurs over a 4 to 8-hour period, with 70% of the ova being shed over a relatively short span of time. These oocytes supposedly give rise to more developed embryos at Days 10 to 12 which advance the uterine environment and reduce survival rates of less developed embryos because of an asynchronous environment. The aim of this experiment was to reduce embryo mortality by influencing the duration and pattern of ovulation. Crossbred gilts (n = 98) were bred at their first observed estrus after being exposed to boars at 200 days of age. Estrus detection was carried out daily at 0000, 0800 and 1600 hours. All gilts were artifically inseminated with fresh semen, with a minimum of 2.7 billion spermatozoa, at both 16 and 32 hours after detection of estrus. Gilts were randomly assigned to one of the following treatments at detection of estrus: 1) 500 IU (2ml) chorionic gonadotrophin (hCG) injected intravenously at the onset of estrus (n = 22); 2) 16 mug (4 ml) gonadotrophin releasing hormone (GnRH) injected intravenously at the onset of estrus (n = 25); 3) 11.5 mug estrogen added to the semen at the time of AI (n = 25); 4) control, untreated gilts (n = 26). All gilts were slaughtered at Day 30 of gestation (Day 0 = day of detected estrus). The mean (+/-SEM) number of ovulations in pregnant gilts per treatment was 13.0 +/- 0.52, 12.6+/-0.51, 13.6+/-0.54 and 13.3+/-0.52, while the mean (+/-SEM) number of normal embryos per treatment was 10.3+/-0.67, 10.5+/-0.66, 10.3 +/- 0.69 and 10.5 +/- 0.67 for hCG, GnRH, estrogen and control groups, respectively, for an embryonic survival rate of 80 +/- 4.2%, 83 +/- 4.1%, 74 +/- 4.3% and 79+/-4.2% in pregnant gilts. If nonpregnant gilts are included, the embryonic survival rate for treatments 1 to 4 was 76+/-7.0%, 73+/-6.5%, 60+/-6.5%, and 64+/-6.4%, respectively. There was no significant difference between treatments for any of these variables. There was no evidence that administration of hCG, or GnRH at the onset of estrus, or the addition of estrogen to semen improved embryonic survival in gilts by Day 30 in this experiment.     

Delayed puberty in gilts in total confinement

Two hundred fourteen crossbred gilts, born in January through March and June through July of two different years, were raised in total confinement until 100 to 120 days of age and then moved to an outside dirt lot (non-confined) or to a single pen in a confinement, finishing building (confined). Beginning at 150 days of age, estrus was checked daily with a boar to determine percentage of gilts that attained puberty and age at first estrus, and weekly blood samples were collected and analyzed for progesterone by radioimmunoassay to determine age at first ovulation. In the Jan.-Mar. born gilts, 75.4% of the non-confined gilts and 37.4% of the confined gilts attained puberty by 270 days of age (P<.001). Although differences were not significant in the gilts born in June-July, more non-confined gilts (62.6%) than confined gilts (50.9%) attained puberty. Of the 121 gilts that ovulated, only 1 non-confined and 3 confined gilts did not exhibit estrus. Average age at first estrus or at first ovulation were similar for confined and non-confined gilts. Adrenal gland weights at 250 to 270 days of age were similar also for confined and non-confined gilts. Based on the results of this study, we conclude that total confinement housing can reduce, by as much as 50%, the proportion of gilts that attain puberty by 8 to 9 months of age and that time of year may influence the extent of delayed puberty.     

Time of ovarian follicle selection during the porcine estrous cycle

Two experiments were conducted to: 1) determine the time during the procine estrous cycle when compensation in ovulation rate after unilateral ovariectomy (ULO) ceases to be complete, 2) compare the follicle selection process in gilts selected for high ovulation rate with unselected control gilts and 3) determine the number of follicles on the right ovary at various stages of the estrous cycle. Experiment I included 25 crossbred gilts, while Experiment II included 17 gilts selected for high ovulation rate and 16 unselected control gilts. The right ovary was removed via a mid-ventral laparotomy on either day 13, 15, 17 or 19 of the cycle. In Experiment I, compensation in ovulation rate ceased between days 13 and 15; whereas, in Experiment II, cessation occurred between days 15 and 17. Selected and control gilts responded alike to ULO, indicating similarity in the follicle selection process. Follicle numbers in the right ovary showed a general decline, especially between days 17 and 19, indicating that atresia was occurring during the follicular phase. The results indicate that the selection of ovarian follicles for ovulation at the ensuing estrus occurs before day 17 of the porcine estrous cyle.